Barnaby Joyce has denied putting a $5 billion price tag on the Nationals' support for a net zero carbon emissions target ahead of a major international conference.

The deputy prime minister is remaining tight-lipped about his climate change action negotiations with Scott Morrison.

Mr Joyce said securing the green light to extend the inland rail from Toowoomba to Gladstone, which could cost up to $5 billion, was not a condition.

He believes being able to show regional voters climate action will not affect jobs is more important than "some price tag for some piece of infrastructure".

But he did note the potential for emissions to be reduced through the project, which could carry the same amount of freight as 110 B-double trucks via the rail system.

Australia is under immense global pressure to sign up to a net zero by 2050 target before November's United Nations climate conference in Glasgow.

Many developed nations have already announced more ambitious targets, while key allies continue to urge Australia to do more.

But climate tensions remain within the coalition after Mr Joyce returned to the leadership on a platform of opposing a net zero target.

Mr Joyce said scientists were providing views to the prime minister and the junior coalition partner about what new climate targets would mean for jobs.

"Those views will then be taken back to members of the National Party room and they can have their deliberations over it," he told ABC radio on Monday.